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The most energy efficient dust collector heating method --- Full steam heating technology

2016-10-28

Introduction to Full Steam Heating Technology of Low and Low Temperature Electrostatic Precipitator

本文对除尘器的加热现状和存在的问题进行了全面分析,提出来系统性的蒸汽加热解决方案。 Abstract: This article analyzes the current status and existing problems of dust collector heating, and proposes a systematic steam heating solution. This solution uses the auxiliary steam of the power plant as the heat source, and gradiently heats the dust ash bucket, ash bucket gasification wind, and insulator purge wind. While ensuring the heating temperature, the condensate temperature is reduced to 60-90 ° C to achieve steam thermal energy. The maximum utilization rate, and make the condensate water fully recycled. This solution is the most economical heating solution for low and low temperature electrostatic precipitators, and it is worth popularizing and applying.

1 Introduction

With the advancement of energy saving and emission reduction in the power industry, more and more units have been or are transforming the original conventional dust collectors into low and low temperature dust collectors. The ash bucket, ash bucket gasification wind, and insulator box of the conventional dust collector need to be heated, and the heating power is less than 500KW, which is not very large. However, if the temperature of the flue gas is reduced to near the dew point, the dry ash in the flue gas will become moist, and the fluidity will become worse, which will make the ash bucket difficult to ash and have a certain corrosiveness, so the heating power of the ash bucket must be greatly increased. On the other hand, the low-temperature flue gas will stick to the inside wall of the porcelain jacket or the surface of the porcelain shaft with low temperature and condensation. Even if the outer wall of the porcelain jacket is heated to a higher temperature, because the porcelain jacket wall is very thick and ash is accumulated, As a result, the inner wall temperature becomes lower and lower, and eventually the heating effect will be lost. This will reduce the insulation performance of the insulator and even cause creepage. Therefore, the insurance method is that the ash bucket heating height reaches 2/3 of the cone, the insulator uses a hot air to heat the outer surface, and then the inner surface of the porcelain sleeve is purged to prevent creepage.

Judging from the current heating status of the low and low temperature dust collectors, the ash hoppers basically use steam heating, mainly because steam heating saves energy and the temperature in the heating area is uniform. The heating method is coil heating, which is saturated and hydrophobic, and the steam consumption is very large. The condensed water has a large amount of flash steam, which is difficult to recover. Most insulators are still electrically heated. Due to the need for power saving, the designed air volume and electric power are small, so the heating temperature is low. Due to the need of the heating temperature of the insulation room, the operating personnel can only turn off the inlet air. As a result, the blowing air is virtually empty, and there is a large safety hazard in long-term operation. Although the insulators of some units use steam-heated hot air sweeping, the power of the heat exchanger is relatively small, which can only ensure the rated heating temperature at a small air volume, and the number of insulators is large. Even airflow is impossible. The uneven air volume distribution will cause the air volume at some purge points to be too small to meet the heating requirements.

The best way to solve the above problems is to use a fully optimized steam heating scheme to steam heat the ash bucket, the ash bucket gasification wind, and the insulator purge wind, completely replacing electric heating. This not only ensures the heating requirements of the low-temperature and low-temperature dust collector, but also greatly reduces the steam consumption, and does not require power consumption, which is the most economical. This is the complete steam heating scheme of the low and low temperature dust collector introduced in this article.

2.Basic requirements for low and low temperature dust collector heating

2.1 Ash hopper heating

The flue gas temperature of low- and low-temperature dust collectors is generally lower than 90 ° C, and the dew point temperature of coal-fired units with 0.5-1% sulfur content is 85-100 ° C. Therefore, the flue gas temperature of low- and low-temperature dust collectors is generally at the dew point temperature nearby. In order to prevent the adhesion and corrosion of ash, the heating temperature of the ash bucket wall should be higher than the acid dew point temperature by more than 10 ° C. Therefore, the heating temperature of the ash wall is generally required to be 100-120 ° C. The heating surface is generally 2/3 of the hopper height above the hopper cone.

The power of the ash bucket is related to the size of the ash bucket, the temperature of the flue gas, the ambient temperature, and the thermal insulation status. The usual design power is 15-20KW / ash bucket.

2.2 Ash bucket gasification wind heating

The function of the ash bucket gasification wind is to fluidize the accumulated ash in the ash bucket, prevent compaction and smooth ash discharge. The electric precipitator generally uses an electric heater, equipped with a roots blower, and sends the hot air heated to 120-150 ° C to the gasification wind pipe of the precipitator, and then enters the precipitator from the gasification plates on both sides of each hopper cone. Inside the ash bucket. The air volume of the gasification wind is small, each ash bucket is about 30-40Nm3 / h, so the ash bucket gasification wind heating power of each 600MW unit dust collector ranges from 50-100KW, which is related to the number of ash buckets.

2.3 Insulator purge air heating

The heating power of each insulator of a conventional dust collector is 1-1.5KW. Because the flue gas temperature is 100-120 ° C, the insulator usually only needs to be heated when the ambient temperature is low. The flue gas temperature of the low- and low-temperature dust collector is usually lower than 90 ° C, which is near or below the dew point temperature. Therefore, the insulator chamber must be continuously heated, and the surface must be purged to prevent dust and condensation. Hot air blowing prevents insulators from creeping in three ways: first, the hot air heats the outer wall of the porcelain sleeve to prevent air condensation on the outer surface; second, the hot air sweeps the inner surface, which can clean the inner wall surface of the porcelain sleeve to prevent dust and acid mist from adhering ; Again the hot air enters the inside of the porcelain sleeve, forming a weak air flow to the porcelain sleeve dustproof cylinder, which can prevent smoke from entering the porcelain sleeve, greatly reducing the smoke concentration in the porcelain sleeve, and also greatly reducing the dew point temperature of the internal gas. . Therefore, as long as the hot air entering the insulator reaches about 100 ° C, even if the acid dew point temperature of the flue gas in the dust collector is high, the gas dew point temperature in the porcelain sleeve is not high, and no condensation will occur on the inner wall, which can ensure the low and low temperature dust collector. safe operation. The insulator purging of the wet electrostatic precipitator can illustrate this reason. The flue gas temperature of the wet dust collector is already below the water dew point. Its insulator is blown by hot air with a temperature of only 60-70 ° C. Because the air volume is much larger than the dry dust collector, there is no wet smoke in the porcelain sleeve, which can be safe. run.

It can be seen that the hot air purging of the insulator is very necessary. In the case of an average air volume of about 45 Nm3 / h, the hot air temperature can be maintained at about 100 ° C.

3. Full steam heating scheme

The complete steam heating scheme refers to the use of steam for the low-pressure heating of the entire low and low temperature electrostatic precipitator. The specific scheme is:


After the auxiliary steam passes through the decompression device, the pressure is maintained at 0.7-0.9 MPa. The dust hopper of the dust collector is first heated so that the temperature in the heating area of the ash hopper reaches 100-120 ° C. The saturated water or soda-water mixture heated by the ash hopper enters the ash hopper gasification steam steam heater and the insulator purge steam steam heater, and the temperature of the gasification wind and the purge wind is heated to 130-150 ° C. The super-cooling temperature of 70-90 ℃ is discharged, and it enters the boiler and starts to expand the container water tank for recycling. As shown in Figure 1.

Figure 1 Schematic diagram of the complete steam heating system of a typical low and low temperature electrostatic precipitator

The difference between this scheme and the ordinary steam heating scheme is that the saturated saturated water heat energy under pressure is further utilized, and finally discharged as low-temperature water with a large degree of subcooling. The heat energy utilization rate of the steam can reach 90%, so the steam consumption Significantly reduced. Supercooled drainage does not generate flash steam, which is convenient for recycling.

3.1 Ash bucket steam heating scheme

Ash bucket steam heating is not different from ordinary steam coil heating, but the arrangement is slightly different. The coil used is usually a light pipe coil with an arrangement height of 2/3 the height of the ash bucket above the cone. However, for some ash buckets with complicated mechanisms, coils with finned tubes can also be used in order to arrange a larger heat dissipation area in a smaller layout space.

The heat transfer between the coil and the wall of the ash bucket is essentially a combination of natural convection and low-temperature radiation heat transfer pairs. It is impossible for the disc tube as a radiator to conduct heat transfer with the wall of the flat ash bucket. Hangzhou Dika Company adopts the patented technology that has been proven in practice. The specific method is to use small diameter and small pitch coils. The outer surface of the coils is kept at a certain distance from the wall of the ash bucket. A certain distance outside the coils is covered with aluminum foil. Finally cover the insulation layer. This arrangement with mezzanine space can maximize the role of natural convection, and the high reflectivity aluminum foil can strengthen the low-temperature radiation heat transfer of the coil. Therefore, the total convective radiation heat transfer coefficient can reach 15W / m2 * ° C. The coil is made of carbon steel, and no paint is needed, because ordinary paint cracks and crusts at high temperatures, which will seriously affect heat transfer. If paint must be applied, only high emissivity heat-resistant paints with a temperature resistance above 200 ° C can be used.

3.2 Ash bucket gasification wind and insulator purge wind heating scheme

The steam of 0.7-0.9MPa has a saturated water temperature of 170-180 ° C. If it is saturated and drained by a trap, it will produce more than 15% of flash steam, which wastes energy and has visual pollution. The ash gasification wind and insulator sweeping wind need to be heated above 130 ° C, which can just use the sensible heat of saturated water. Therefore, Hangzhou Dika's complete steam heating solution is to introduce the high-temperature saturated water heated by the ash hopper into the ash hopper gasification wind and insulator purge wind steam heater, and finally become 70-90 ℃ supercooled water to be discharged. Because the thermal power of saturated water is less than the heating power of gasification and purge air, some steam needs to be supplemented. The heat source that enters the gasifier and purge steam heater is actually a steam-water mixture.

Hangzhou Dika's ash bucket gasification wind and insulator purge wind steam heater is an efficient and safe soda-air heating device, which can simultaneously satisfy the cooling of saturated water, soda-water mixture, steam and other media. In the form of emissions. The heat exchange element of the heater is a thick-walled stainless steel-aluminum finned tube, which is durable. The heater has its own adjustment device and local instrument. In addition, the heating device is also equipped with a security control system to monitor the temperature and humidity of cold and hot air in real time, determine whether a soda leak has occurred, and take measures.


The purge air steam heater is arranged under the dust collector. Generally, two heaters are used, and they are used at the same time and are reserved for each other. Under normal use, it is low-temperature and super-cooled drainage. If there is one troubleshooting, the other can increase the heating power greatly by increasing the drainage temperature, so that it can meet the heating requirements of blowing air to a minimum. The fan is also dual-use and one-ready or one-use and one-ready. The hot air is sent to the top of the dust collector through a main air pipe, and then distributed to the insulation room. For 1000MW units, in order to reduce the uneven distribution of purge air, it is best to use 4 heaters and two main air ducts.

In order to ensure the effective heating of the insulator by the blowing air, it is best to use a ring-shaped blower to blow the outer surface of the porcelain sleeve, and modify the air inlet of the porcelain cover to ensure the necessary resistance loss and uniform sweeping of the inner wall. The hot air sweep of the insulation room is shown in Figure 2.

Figure 2 Schematic diagram of air distribution in porcelain suite rooms

4. The effect of complete steam heating

Hangzhou Dika Company has done full steam heating of conventional dust collectors in power plants such as Beilun and Taizhou, and has done full steam heating of low and low temperature dust collectors in power plants such as Yuhuan and Heyuan. Although the electric heating system for electric dedusting is simple and requires little investment, the heating effect and reliability are not good. The service life of electric heaters is generally only 5000-10000 hours. The number of plate heaters on the ash hopper is large, and it is impossible to find that it is broken. Maintenance is difficult. In addition, the heating of the plate heater is uneven, and the temperature of the place without the heater is very low, and the well-welded steam coil is not easy to leak, the reliability is high, and the heating is very uniform.

Take the low- and low-temperature dust collector of Heyuan Power Plant as an example for complete steam heating. The basic parameters are shown in Table 1. The dust collector of Heyuan Power Plant has 32 ash hoppers, and the top is a large insulation chamber structure. In the large insulation room, the purge air is sent to the air distribution pipe of the insulation room through a main air pipe, and finally blown out by a ring-shaped purge pipe of a porcelain sleeve.

Table 1 Complete steam heating parameters of low and low temperature electrostatic precipitator for 600MW unit

Serial number

name

Ash bucket steam heating

Gasification wind steam heating

Purge wind steam heating

1

Heating power (KW)

640

40

280

2

Heating temperature (℃)

110-125

135

135

3

Drainage temperature of each device (℃)

170

80

80

4

Comprehensive drainage temperature (℃)

80-85

5

Steam consumption (kg / h)

1160

0

240

6

Total steam consumption (kg / h)

1400

7

Steam conversion power (KW)

190

8

Energy saving rate

1-190 / 960 = 80%

It can be seen from Table 1 that the heating effect of the complete heating system is still very good. According to testing and calculations, the wind temperature of the ring-shaped air outlet pipe toward the insulator is higher than 110 ° C.

With a steam consumption of 1400kg / h, it replaces the electric heating power of 960KW. Considering that these steam can generate a maximum of 190KW of electricity, when converted into electric heating, the energy saving rate can reach 80%. If the ordinary steam heating scheme is adopted, the fully saturated drainage requires 1750kg / h of steam, which increases the steam consumption by 350kg / h than the high-efficiency heating system, with an increase rate of 25%.

5. Energy saving ideas of existing steam heating systems

At present, the ash buckets of many low- and low-temperature electrostatic precipitators for many generator sets have been heated by steam, but the ash bucket gasification wind and insulator purge wind are still heated by electricity. The consumption of steam and electricity is very large and very uneconomical. If the complete steam heating scheme is used for reconstruction, the existing ash bucket steam heating system can be used, and only the high-temperature condensed water heated by the ash bucket needs to be drawn out, and the gasification wind and purge wind steam heater are passed in, and then the total wind The pipe can send the hot air to the original purge port, and the reconstruction amount is small. In order to obtain a satisfactory heating effect, it is necessary to appropriately modify the purge port of the insulation chamber and install a ring-shaped blower tube outside the porcelain sleeve. In this way, the electric heating can be completely replaced, and the high-temperature drainage sensible heat heated by the ash hopper can be fully utilized, and the economy is significantly improved.

6. Economics of complete steam heating

Full steam heating is the most energy-saving and economical heating method for conventional electric precipitators and low-low temperature electric precipitators. Assume that a 600MW unit has 32 ash buckets, a 40KW gasification wind heater, and 136 insulator electric heaters. If it is to be a low and low temperature dust collector, the heating power of each ash bucket is about 20KW. The blowing air heating power is about 2KW. Table 2 is an economic comparison table for the three cases.

1). All use electric heating. At this time, the power of electric heating reached 960KW.

2). Partial electric heating and part steam heating. Ash hopper steam is usually used to heat the rest. At this time, the steam heating power is 640KW and the electric heating power is 320KW.

3). Complete steam heating. At this time, the electric heating power is 0, and the steam heating power is 960KW.

Table 2 Economic comparison of different heating methods

Serial number

name

All electric heating

Partial electric part steam heating

Full steam heating

1

Total heating power (KW)

960

960

960

2

Electric heating power (KW)

960

640

0

3

Steam heating power (KW)

0

320

960

4

Annual running time (h)

7000

7000

7000

5

Annual electric heating energy consumption (10,000 kwh / a)

672

224

0

6

Annual steam heating consumption (t / a)

0

8120

9800

7

Annual converted power consumption (10,000 kwh / a)

672

224 + 45

133

8

Cost of electricity price (yuan / kwh)

0.4

0.4

0.4

9

Annual heating cost (ten thousand yuan)

269.6

107.6

53.2

It can be seen from Table 2 that the annual heating cost of complete steam heating is only about 1/5 of the total electric heating cost, and only 1/2 of the partial electric heating cost.

7. Summary

From the above analysis, it can be known that the complete steam heating scheme of the low-temperature and low-temperature dust collector fully reflects the characteristics of high efficiency and safety of steam heating, which can well meet the heating requirements and reliable performance. The scheme utilizes gradient heat energy of steam, which greatly reduces energy consumption and has the best economy. Today, when energy conservation and environmental protection are promoted, if the full steam heating technology can be fully promoted, the annual economic and environmental benefits are very considerable.

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